Part of the comercial bumblebees used to pollinate crops forage outside the greenhouses, on wild plants located in the closest areas. Most alarming, almost half of these bumblebees carry parasites with the potential to be transmitted to other bee species and also feed on similar plants. The study has been conducted by the Doñana Biological Station (EBD-CSIC), the Autonomous University of Barcelona and the University of Almería. It took place in natural areas of the Cabo de Gata - Níjar region, in the province of Almería, and has been published in the international journal Agriculture, Ecosystems & Environment.
Over two million commercial bumblebee colonies are used on an annual basis to pollinate around 20 crop types worldwide. Despite their use, especially with crops grown in greenhouses, there is mounting evidence that many individuals also forage outside of them and could risk the ecological balance in the closest natural areas. "The use of commercial pollinators could help improve crops, however, it can also generate an unwanted impact on the environment through competition for flower resources between native and introduced species or the transmission of pathogens that could reduce the native populations", explains Montserrat Vilà, research professor at Doñana Biological Station and one of the authors of the study.
Alejandro Trillo, another author of the study that is currently working at Doñana Biological Station, observed during 75 hours over 3400 pollinators visiting wild plants in Cabo de Gata. Besides, 101 bumblebees were observed, most of them (95%) foraging within a radious of less than 200 meters from the greenhouses. "This data is positive and could indicate that the area of influence of this introduced species is limited –at least to date-. However, this does not guarantee that naturalized bumblebee colonies are present in the area, as we observed in other regions such as Huelva", explains the researcher.
The 41% of these commercial bumblebees analyzed had high parasite prevalence. Although there is no native bumblebees in these areas, some of the parasites affect to other pollinator species, such as honeybees, the most abundant pollinator present in all plots. Besides, the scientists detected that they feed on the same plants than other pollinators. Despite the presence of bumblebees in these natural areas, the study could not find a significant relationship in pollinator abundance and diversity with respect to bumblebee abundance in natural areas.
The abundance of commercial species plays an important role in the degree of competition with native pollinators. The fact that bumblebees are scarce and restricted to the closest areas of greenhouses implies that wild pollinators are not significantly impacted. Despite this, the scientific team could not discard the existence of less noticeable effects related to pathogen transmission or the direct competence with specific species. "Actions like preventing commercial bumblebees from escaping greenhouses, accurately control their health when they are raised by companies and optimise their use should be considered to minimize future risks", concludes Montserrat Vilà.
Alejandro Trillo, Ignasi Bartomeus, F. Javier Ortiz-Sánchez, Jordina Belmonte, Montserrat Vilà (2021). No detectable impact of parasite–infected commercial bumblebees on wild bees in areas 1 adjacent to greenhouses despite diet overlap. Agriculture, Ecosystems & Environment. Doi: https://doi.org/10.1016/j.agee.2021.107604https://doi.org/10.1016/j.agee.2021.107604